Laser sintering is one form of additive manufacturing that fabricates three-dimensional objects from digital data. As known in the art, laser sintering heats layers of powder, typically a polymer or a metal, with a laser to cause the powder particles to fuse to one another in predetermined patterns to define the cross-sectional layers of the object being fabricated. Such techniques are disclosed in U.S. Pat. Nos. 4,863,538; 5,155,321; 5,252,264; 5,352,405; 6,815,636; 7,569,174; and 7,807,947, the disclosures of which are incorporated by reference herein in their entirety.
One problem with laser sintering is laser attenuation during the build process whereby the laser power at the image plane (the surface of the sinterable powder being exposed to the laser beam) changes (typically decreases). Such change in laser power may be due to a number of issues and can lead to parts being different colors from the bottom to the top (along the z-axis) or having different mechanical properties along the z-axis.
Another problem with laser sintering, particularly with polymers that are heated to near the melting temperature, is that the sinterable powder that is not fused can be reused only a certain number of times before the powder produces parts with undesirable quality (such as “orange peeling” on the surface), coloration, or reduced mechanical properties. The result is that operators of laser sintering machines must dispose of a certain amount of used laser sintering powder to maintain part quality.